One-piece mechanical filter having portions forming plural resonators and coupling means



3,185,943 PORTIONS FORMING ONATORS AND COUPLING MEANS y 25, 1965 SEllCHl HONDA ETAL ONE-PIECE MECHANICAL FILTER HAVING PLURAL RES Original Filed April 16, 1957 2 Sheets-Sheet l yuza 447216 251104 W flz orngz y 25, 1955 SEIICHI HONDA ETAL 3,185,943

ONE-PIECE MECHANICAL FILTER HAVING PORTIONS FORMING PLURAL RESONATORS AND COUPLING MEANS Original Filed April 16, 1957 2 Sheets-Sheet 2 direction 0/ I I: i0 exciting point matian gwave resonato l mm r i ii rf i7 15 v 2194' Ego/(9(0) directivn of motion we 0 K5 attenuation loss I I I I I I I E i H e uenc y f-x Io II fr Q Y United States Patent 3,185,943 ONE-PIECE MECHANICAL FILTER HAVING POR- TIONS FORMING PLURAL RESONATORS AND COUPLING MEANS Seiichi Honda, Hitachi-shi, Ibaragi-ken, and Yuzo Nakazawa, Kawasaki-ski, Kanagawa-ken, Japan, assignors to Toyotsushinki Kabushiki Kaisha (known as Toyo Communication Equipment Co., Ltd.), Kawasaki-shi, Japan Original application Apr. 16, 1957, Ser. No.653,190, now Patent No. 3,015,789, dated Jan. 2, 1962. Divided and this application Dec. 29, 1961, Ser. No. 188,291 3 Claims. (Cl. 333-72) Thi application is a divisional application of U.S. patent application Ser. No. 653,190, filed April 16, 1957, now US. Patent 3,015,789, issued January 2, 1962, and is entitled to the benefit of the priority dates of the first patent application under 35 U.S.C. 120.

This invention relates to an improvement of a mechanical filter.

An essential object of this invention is to provide a mechanical filter having a remarkably sharp cut-ofi? frequency character.

Another object of this invention is to provide an electromechanical filter having a sufiicient mechanical strength while employing members made of relatively weak quartz crystal, having remarkably sharp cut-off frequency char acteristics.

The principle, construction and operation of this invention, together with further objects and advantages thereof, may best be understood by reference to the folowing description, taken in connection with the accompanying drawings, in which:

FIG. 1(a) is a perspective view of an example of this invention, in which five elements are cascaded.

FIG. l( b) is a perspective view showing a modification of the example in FIG. 1(a).

FIG. 2(a) and FIG. 2(1)) are perspective views showing, respectively, other modifications of the examples in FIG. 1(a) and FIG. 1(b).

FIG. 3 is an equivalent electrical circuit diagram of the examples in FIGS. 1(a), 1(1)), 2(a) and 2(1)).

FIG. 4 is a perspective view of an element having the simplest construction of a further example of this invention.

FIG. 5 is a schematic connection view of this invention, in which the elements illustrated in FIG. 4 are used as the essential elements.

FIG. 6 is an equivalent electrical circuit diagram of the example in FIG. 5. 7

FIG. 7 (a) is a perspective view of a part of the example in FIG. 7( b).

FIG. 7(1)) is a perspective view of a still further example of this invention.

FIG. 7(0) is an equivalent electrical circuit diagram of the example in FIG. 7(b).

FIG. 8(a) and FIG. 9(a) are perspective views of two other examples of this invention.

FIG. 8(1)) and FIG. 9(1)) are equivalent electrical circuit diagrams of the examples in FIGS. 8(a) and 9(a), respectively.

FIG. 9(c) is a perspective view of a modification of the example in FIG. 9(a).

FIG. 10 is a frequency-attenuation characteristic of the example in FIG. 8(a).

In the drawings, the same members are indicated by the same numerals or symbols.

Each of the mechanical filters illustrated in FIGS. 1(a) and 1(b) is composed of transducers 1, resonators 2, and couplers 3, which are formed as one block by cutting olt piezoelectric material such as a quartz crystal piece.

3,185,943 Patented May 25, 1965 Each of the mechanical filters illustrated in FIGS. 2(a) and 2(b) is composed of transducers 1, resonators 2, and couplers 3, which are coupled in cascade so as to form a block of five stages, the said transducers and resonators being made of a material such as quartz crystal and the said couplers being made of a suitable material.

The members 1 and 2 form the quartz crystal vibrators, vibrating usually in the longitudinal mode, and the orientations thereof are selected so as to accommodate to the desirable frequency and temperature characteristics of the said members. Of course, determination of the orientations and forms of the said members 1 and 2 may be modified in accordance with the vibration modes such as longitudinal vibration, bending vibration, torsional vibration, thickness vibration, lateral vibration and the like.

The transducer 1 and the resonator 2 have the same form. They are plated on both the front and rear surfaces thereof, as indicated by oblique lines, to make electrodes on the said surfaces. A solder cone 4 is attached to the vibration nodal point of each said surface and at these points are soldered supporting lead wires 5 which are the electrical terminal of said electro-mechanical filter. The coupler 3 is connected to a point near the nodal point of vibration of the transducer and resonator. In the conventional mechanical filter, for the purpose of obtaining a narrow band pass filter, the sectional area of the coupler must be selected to be very narrow, thus causing the filter to be mechanically weak.

However, when the connection is made at the point near the nodal point, rather than at the nodal point, as in the case of this invention, use of the coupler having a large sectional area for the narrow band pass filter is made possible. Consequently, even when mechanically weak material such as a quartz crystal is used as the coupler, it has strength sufiicient for practical use.

The equivalent electrical circuit of the mechanical filter of the five stage type illustrated in FIGS. 1(a), 1(1)) and FIGS. 2(a), 2(12) can be indicated as shown in FIG. 3, in which the members m and s, are, respectively, an equivalent mass and an equivalent stiffness which form a series resonance circuit, the said resonance circuits being coupled by a stiifness s and a transducer having an electromechanical conversion rate 1:A being connected with each of two ends of the resultant equivalent circuit.

The operation and character of the circuit in FIG. 3 in the case of about resonance frequency will be described in the following in connection with a band pass filter.

When the cut-off frequencies, center frequency, terminal impedance, and damped capacity of the transducer are taken, respectively, as f and f f /f -f r and C the following equations will be obtained.

r will be obtained. 0

When the resonators vibrate in the longitudinal direction, the equivalent lumped constants m and s of a 3 mechanical resonator of /2 wave length will be given by the following equations.

where S and E are, respectively, sectional area, length of vibrating direction, and rigidity modulus of the coupling stiffness.

'In the example in FIG. 1(a), when the filter carries out a lateral vibration, the coupling stiffness is determined by the coupling point of the coupler with the resonator.

For instance, when the resonators are coupled by the couplers in such a manner that vibration force is trans mitted to the next resonator by the length of vibrating direction of the coupler at the neutral surface of the vibration nodal point of the resonator, the coupling stiffness s will be indicated by the following equation.

J Ma *12 b, 1,

where G, 1 b and t are, respectively, rigidity modulus, length of vibrating direction, width of the coupler and thickness of the coupler illustrated in FIGS. 1(a) and 1(1)).

As will be seen from the Equations 2, 4 and 5, it is easily possible to make the bandwidth narrow or wide by suitable selection of the relative positions between the couplers and resonators, and their dimensions.

In FIG. 4 is shown a simple mechanical filter Q of two stage type according to this invention. Such a mechanical filter of few stage type is simplest in its construction and can be made of a small quartz crystal piece. The mechanical filter illustrated in FIG. 4 may be used for obtaining an electro-mechanical filter by combination of electrical circuits 6, 7 and 8 with the said filters Q, as shown in FIG. 5. The said combined circuit can be indicated by the equivalent circuit as shown in FIG. 6, the inductances and capacitances of the said electrical circuit being, of course, determined by the bandwidth and characteristic impedance of the band pass filter to be constructed.

The above-mentioned mechanical filters of this invention relate to the filter, the equivalent circuits of which are of constant K type and the like. However, the filter of this invention may be applied for the mechanical filter such as the so-called derived M type filter having attenuation poles in the attenuation frequency regions.

The attenuation per stage in the above-mentioned mechanical filter is generally indicated by the following equation.

where m and wn indicate, respectively, the cut-off angular frequencies.

In the constant K type filter, six or more stages should be coupled in cascade in order to obtain the desired attenuation in the vicinity of cut-otf frequency for ordinary use.

eoth m /1 92 where m and we indicate, respectively, the center angular frequency and Q value at the attenuation pole.

The smaller the factor 112 is selected, the nearer the attenuation pole can be brought to the cut-off frequency, whereby a sharp cut-off attenuation characteristic can be obtained.

When such an elastic piece 9 capable of being vibrated longitudinally as shown in FIG. 7(a) is excited at any point except the end points and center point thereof (i.e. dissymmetrically excited), two kinds of antiresonance frequencies determined by the elemental pieces corresponding to the lengths l and 1 are produced.

By combination of the antiresonators 9 as described above with a parallel resonator 16 at the positions corresponding to /2 wave length 1 a derived M type mechanical filter as shown in FIG. 7(b) can be constructed, the equivalent electrical circuit of the said filter being indicated in FIG. 7(a).

The pass bandwidths in the circuit in FIG. 7(a) can be, when the bandwidths are narrow, indicated approximately by the following equations.

b w w m o where w and w L1, and w, and m indicate, respectively, cut-off angular frequencies, attenuation pole angular frequencies and center angular frequency.

When the equation is put in the Equation 8, the characteristic impedance is indicated by r and the conditions B 1 and b l are adopted, the values of the elements in the circuit in FIG. 7(c) will be indicated by the following equations.

but

where A p and E indicate, respectively, the sectional area, density, and rigidity modulus of the resonator.

By coupling two of the said antiresonators 9 with a resonator having /2 wave length as shown in FIG. 7(1)), the derived M type filter such as shown in FIG. 7(c) will be obtained.

Furthermore, if sectional area, density and rigidity modulus of the resonator 10 of /2 Wave length are indicated, respectively, by A p and E the following equations will be obtained.

2 m A l 2 When all parts composing the filter are made of same material, particularly of quartz crystal, the construction thereof becomes simple according to the following equa- In the example in FIG. 8(a), the equivalent circuit thereof being shown in FIG. 8(b), the transducer 11 made of quartz crystal is plated on both surfaces thereof with metal to form two electrodes and a supporting lead wire 12 is soldered to each electrode thereof. The resonators 13 and the coupler 14 are also made of quartz crystal vibrator. The coupling positions between the adjacent resonators should differ in accordance with the vibrating modes of the mechanical filter. However, it is generally preferable to couple the said members at a position somewhat separated from the vibration nodal point so as to obtain a resonator capable of operating as the resonator having two antiresonance frequencies.

The bandwidth can be determined by the relative relations between the coupler 14 and the dimension of the resonator 13.

In the case of the mechanical filter illustrated in FIGS. 8(a) and 8(1)), it is excited at the position within the width corresponding to the length 1 of the coupler 14 (but, l ,,=l=I so that when the following stages are successively excited along the said width with a uniform force, two antiresonating circuits are obtained, whereby a circuit similar to the circuit of the derived M type filter will be obtained.

In FIG. 9(a) is shown a modification of the mechanical filter illustrated in FIG. 7(b), the equivalent electrical circuit thereof being indicated in FIG. 9(b).

In FIG. 9(a), the filter is made by combination of the exciter 15 capable of transmitting longitudinal vibration towards the longitudinal direction of the filter, series resonators 16 of /2 wave length, and couplers 17 of /2 wave length, the said filter corresponding to the combined filter of the series resonators 16 with an antiresonator composed of two elements 18 and 19.

The equivalent electrical circuit of the filter in FIG. 9(a) is shown in FIG. 9(b), in which the lumped elemental constants corresponding to the resonators 16 and couplers 17 are indicated, respectively, by m,;, .9 and m s and the equivalent masses and the equivalent stiifnesses of two antiresonators are indicated by m m and s and s respectively.

The equivalent electrical circuit additionally contains the factors m and 5 as compared with the normal derived M type. For the manufacture of constant K type filter by combination of the factors m s with m s the width 11 of the resonator 16 should be selected so as to be extremely larger than the width ha of the coupler 17. However, when the difference between the width of the resonator 16 and that of the coupler '17 is not remarkably large, the influence due to the factors 111 and s is not too large, so that the constant K type is not established and the derived M type filter is made possible.

The example in FIG. 9(a) corresponds to the mechanical filter obtained by shortening the length 14 of the resonator 16 of the example in FIG. 9(a). When the filter in FIG. 9(a) is used, the influences due to m and S in FIG. 9(1)) can be more remarkably reduced.

The characteristic curve in FIG. 10 indicates the frequency-attenuation characteristic of the derived M type mechanical filter. The said curve indicates that the frequencies La and fw have, respectively, attenuation poles.

-As will be clearly understood from the above description, since the transducers and resonators of the mechanical filter of this invention are made of quartz crystal vibrator, frequency adjustment in the case of manufacture of the elements becomes very easy and accurate and, particularly excellent temperature characteristic and aging characters are obtained.

While we have described particular embodiments of our invention, it will, of course, be understood that we do not intend it to be limited thereto, since many modifications may be made and we, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

We claim:

1. An electro-mechanical filter comprising a plurality of resonators, means coupling said resonators in series and means coupling a transducer to each end resonator of the series, the resonators, transducers and coupling means being a single quartz element,

wherein each said coupling means is connected to the adjacent resonators at points adjacent the nodal points of vibration of each said element.

2. A device as in claim 1 wherein said resonators are rectangular and the coupling means are connected to the edges of each rectangular element.

3. A device as in claim 1 wherein said resonators are stacked and rectangular and the coupling means are connected to the faces of each rectangular element.

References Cited by the Examiner UNITED STATES PATENTS 2,276,013 3/42 Bohannon 333-72 2,345,491 3/44 Mason 333-72 2,406,796 9/46 Bies 333-72 2,443,471 6/48 Mason 333-71 2,501,488 3/50 Adler 333-71 2,647,948 8/53 Roberts 333-71 2,662,217 12/53 Roberts 333-71 2,769,867 11/56 Crownover 3333-72 2,814,785 11/57 Burns 333-72 2,858,373 10/58 Hellman 333-72 2,877,431 3/59 McSkimin 333-30 2,906,971 9/59 Mason 333-71 HERMAN KARL SAALBAOH, Primary Examiner. 

1. AN ELECTRO-MECHANICAL FILTER COMPRISING A PLURALITY OF RESONATORS, MEANS COUPLING SAID RESONATORS IN SERIES AND MEANS COUPLING A TRANSDUCER TO EACH END RESONATOR OF THE SERIES, THE RESONATORS, TRANSDUCERS AND COUPLING MEANS BEING A SINGLE QUARTZ ELEMENT. WHEREIN EACH SAID COUPLING MEANS IS CONNECTED TO THE ADJACENT RESONATORS AT POINTS ADJACENT THE NODAL POINTS OF VIBRATION OF EACH SAID ELEMENT. 